Electrochemical reduction of surface metal oxides

Abstract

This disclosure relates to methods for reducing metal oxide layers to pure metals using microwave radiation. Specific embodiments provide methods for reducing native metal oxides on metal interconnects within substrate features including dielectric sidewalls. In some embodiments, the surrounding dielectric material is not damaged by the disclosed process.

Description

Electrochemical Reduction of Surface Metal Oxides Embodiments of the present disclosure generally relate to methods for converting surface metal oxides to pure metals. Specifically, embodiments of the present disclosure relate to methods for reducing metal oxides by microwave treatment. Exposing a pure metal material to air causes a thin layer of metal oxide to form on the surface of the metal. This surface layer of metal oxide interferes with the selectivity of subsequent processing steps and increases the resistance of the interconnect. Accordingly, there is a need for methods to prevent and / or remove metal oxides from the surface of metal materials. Although the integration of processing equipment and the transport of wafers under vacuum have reduced the need to remove these metal oxide layers, current pre-cleaning methods typically require hydrogen plasma, high processing temperatures (greater than 300 °C), and / or high-energy argon (Ar) sputtering. However, these processes typically damage adjacent dielectric materials (e.g., feature sidewalls) and have an adverse effect on the selectivity of many metal deposition processes (e.g., selective tungsten deposition). In addition, there is a need to develop and / or adapt current pre-cleaning methods for different metal oxide materials (e.g., WOx, MoOx, CoOx, RuOx, CuOx, etc.). Each different material may require a different plasma source, a different reaction gas mixture or chemical soak, and / or different processing conditions (e.g., temperature, pressure). Accordingly, there is a need for a general method for converting surface metal oxides to pure metals. In addition, there is a specific need for a process that can be performed at relatively low temperatures without damaging surrounding materials. One or more embodiments of the present disclosure relate to a method for reducing a surface metal oxide layer. The method includes the step of exposing the metal oxide layer on the metal material to microwave radiation. Additional embodiments of the present disclosure relate to a method for reducing molybdenum oxide. The method includes the step of exposing a surface of a substrate having at least one feature to microwave radiation to reduce a molybdenum oxide layer on a molybdenum metal material. The at least one feature extends from the surface of the substrate a depth to the bottom of the molybdenum oxide layer and has two sidewalls comprising a low-k dielectric. Before describing several exemplary embodiments of the present disclosure, it is to be understood that the present disclosure is not limited to the details of the structures or processing steps set forth in the following description. The present disclosure is capable of other embodiments and of being practiced or carried out in various ways. As used herein, the term "about" means approximately or nearly and, in the context of the numerical values or ranges set forth, means a variation of ±15% or less of the numerical value. For example, values that differ by ±14%, ±10%, ±5%, ±2%, ±1%, ±0.5%, or ±0.1% will satisfy the definition of "about". As used in this specification and the appended claims, the terms "substrate" or "wafer" refer to a surface or a portion of a surface upon which processing is performed. Those skilled in the art will also understand that reference to a substrate may refer only to a portion of the substrate, unless the context clearly dictates otherwise. Additionally, reference to depositing on a substrate may refer to a bare substrate and a substrate having one or more films or features deposited or formed thereon. As used herein, "substrate surface" refers to any substrate or the surface of a material formed on a substrate on which film processing is performed during a manufacturing process. For example, substrate surfaces on which processing can be performed include materials such as silicon, silicon oxide, strained silicon, silicon-on-insulator (SOI), carbon-doped silicon oxide, amorphous silicon, doped silicon, germanium, gallium arsenide, and any other materials such as metals, metal nitrides, metal alloys, and other conductive materials, depending on the application. Substrates include (but are not limited to) semiconductor wafers. The substrate may be exposed to a pretreatment process to polish, etch, reduce, oxidize, hydroxylate, anneal, and / or bake the substrate surface. In addition to performing film processing directly on the surface of the substrate itself, in this disclosure, any film processing steps disclosed may also be performed on an underlying layer formed on the substrate, as disclosed in more detail below, and the term "substrate surface" is intended to include such underlying layers as indicated by the context. Thus, for example, when a film / layer or a portion of a film / layer has been deposited on a substrate surface, the exposed surface of the newly deposited film / layer becomes the substrate surface. The substrate surface may have one or more features formed therein, one or more layers formed thereon, and combinations thereof. The shape of the features may be any suitable shape, including (but not limited to) grooves, holes, and vias (circular or polygonal). As used in this regard, the term "feature" refers to any intentional surface irregularity. Suitable examples of features include (but are not limited to) grooves having a top, two sidewalls, and a bottom extending into the substrate, and vias having one or more sidewalls extending into the substrate to the bottom. The term "on" indicates direct contact between elements. The term "directly on" indicates direct contact between elements without an intervening element. As used in this specification and the appended claims, the terms "precursor", "reactant", "reactive gas", and the like may be used interchangeably to refer to any gaseous species that can react with the substrate surface. Embodiments of this disclosure advantageously provide methods for reducing surface metal oxides at relatively low temperatures without affecting adjacent materials. Specific embodiments advantageously provide methods for reducing metal oxides using microwave processing. In some embodiments, the metal oxide layer is not exposed to plasma. Embodiments of the present disclosure are depicted by the figures, which show processes, substrates, and apparatuses in accordance with one or more embodiments of the present disclosure. The processes, schemes, and resulting substrates shown are illustrative of the disclosed processes only, and those skilled in the art will recognize that the disclosed processes are not limited to the applications shown. Referring to FIG. 1, a cross-sectional view of an exemplary processing tool 100 is shown. The processing tool 100 can be a processing tool suitable for any type of processing operation that utilizes microwaves. Although the embodiments described in detail herein relate to microwave processing methods, it should be understood that additional processing methods (including plasma processing methods) can also be implemented on the processing tool 100. In addition, it should also be understood that the PEALD method described herein can also be performed using different processing tools. Generally, the processing tool 100 includes a chamber 178. In a processing tool 100 for substrate processing, the chamber 178 can be a vacuum chamber. The vacuum chamber can include a pump (not shown) for removing gas from the chamber to provide a desired vacuum. Additional embodiments can include a chamber 178 that includes one or more gas lines 170 for providing processing gas to the chamber 178 and an exhaust line 172 for removing by-products from the chamber 178. Although not shown, it should be understood that the processing tool can include a showerhead or other gas distribution components for uniformly distributing the processing gas over the substrate 174. In some embodiments, the substrate 174 can be supported on a chuck 176. For example, the chuck 176 can be any suitable chuck, such as an electrostatic chuck. The chuck can also include cooling lines and / or heaters to provide temperature control to the substrate 174 during processing. The processing tool 100 includes one or more microwave sources 104. The microwave source 104 can include a solid-state microwave amplification circuit 130 and an applicator 142. In some embodiments, a voltage control circuit 110 provides an input voltage to a voltage-controlled oscillator 120 to generate microwave radiation at a desired frequency, which is transmitted to the solid-state microwave amplification circuit 130 in each microwave source 104. After being processed by the microwave amplification circuit 130, the microwave radiation is transmitted to the applicator 142. In some embodiments, an array 140 of applicators 142 is coupled to the chamber 178 and each applicator acts as an antenna for coupling microwave radiation to the substrate 174 in the chamber 178. Now referring to FIGS. 2-4, a series of diagrams depicting a microwave processing tool 100 in accordance with an embodiment are shown. The microwave processing tool 100 generates microwaves that can be used for low-temperature reduction of metal oxides. Referring now to FIG. 2, a cross-sectional view of a microwave processing tool 100 (hereinafter simply referred to as the processing tool 100) according to an embodiment is shown. The processing tool can emit high-frequency electromagnetic radiation. As used herein, "high-frequency" electromagnetic radiation includes radio-frequency radiation, very-high-frequency radiation, ultra-high-frequency radiation, and microwave radiation. "High-frequency" can refer to frequencies between 0.1 MHz and 300 GHz. Generally, an embodiment includes a processing tool 100 that includes a chamber 178. In the processing tool 100, the chamber 178 can be a vacuum chamber. The vacuum chamber can include a pump (not shown) for removing gas from the chamber to provide a desired vacuum. Additional embodiments can include a chamber 178 that includes one or more gas lines 170 for providing a processing gas to the chamber 178 and an exhaust line 172 for removing by-products from the chamber 178. Although not shown, it should be understood that gas can also be injected into the chamber 178 through a source array 150 (such as a showerhead) to evenly distribute the processing gas over the substrate 174. In one embodiment, the substrate 174 can be supported on a chuck 176. For example, the chuck 176 can be any suitable chuck, such as an electrostatic chuck. The chuck 176 can also include cooling lines and / or heaters to provide temperature control to the substrate 174 during processing. Due to the modular configuration of the high-frequency emission modules described herein, the embodiment allows the processing tool 100 to accommodate substrates 174 of any size. For example, the substrate 174 can be a semiconductor wafer (such as 200 mm, 300 mm, 450 mm, or larger). Alternative embodiments also include substrates 174 other than semiconductor wafers. For example, an embodiment can include a processing tool 100 configured to process glass substrates (such as for display technology). According to an embodiment, the processing tool 100 includes a modular high-frequency emission source 104. The modular high-frequency emission source 104 can include an array of high-frequency emission modules 105. In one embodiment, each high-frequency emission module 105 can include an oscillator module 106, an amplification module 130, and an applicator 142. As shown in the figure, the applicator 142 is schematically shown as integrated into the source array 150. In one embodiment, the oscillator module 106 and the amplifier module 130 may include electrical components as solid-state electrical components. In one embodiment, each of the plurality of oscillator modules 106 may be communicatively coupled to a different amplifier module 130. For example, each oscillator module 106 may be electrically coupled to a single amplifier module 130. In one embodiment, the plurality of oscillator modules 106 may generate incoherent electromagnetic radiation. Thus, the electromagnetic radiation induced in the chamber 178 will not interact in a way that results in an undesired interference pattern. In one embodiment, each oscillator module 106 generates high-frequency electromagnetic radiation, which is transmitted to the amplifier module 130. After being processed by the amplifier module 130, the electromagnetic radiation is transmitted to the applicator 142. In one embodiment, each of the applicators 142 emits the electromagnetic radiation into the chamber 178. In some embodiments, the applicator 142 couples the electromagnetic radiation to the substrate 174 in the chamber 178. Referring now to FIG. 3, a perspective view of a source array 150 according to one embodiment is shown. In one embodiment, the source array 150 includes a dielectric plate 160. A plurality of cavities 167 are provided in the first surface 161 of the dielectric plate 160. The cavities 167 do not penetrate the second surface 162 of the dielectric plate 160. The source array 150 may further include a plurality of dielectric resonators 166. Each of the dielectric resonators 166 may be located in a different cavity 167. Each of the dielectric resonators 166 may include a hole 165 at the axial center of the dielectric resonator 166. In one embodiment, the dielectric resonator 166 may have a first width Wl, and the cavity 167 may have a second width W2. The first width W1 of the dielectric resonator 166 is less than the second width W2 of the cavity 167. The difference in width provides a gap G between the sidewalls of the dielectric resonator 166 and the sidewalls of the cavity 167. In the illustrated embodiment, each of the dielectric resonators 166 is shown as having a uniform width W1. However, it should be understood that not all of the dielectric resonators 166 of the source array 150 need to have the same dimensions. Referring now to FIG. 4, a cross-sectional view of a processing tool 100 including a component 190 according to an embodiment is shown. In one embodiment, the processing tool includes a chamber 178 sealed by the component 190. For example, the component 190 may abut against one or more O-rings 181 to provide a vacuum seal to the interior volume 183 of the chamber 178. In other embodiments, the component 190 may be interfaced with the chamber 178. That is, the component 190 may be part of a lid that seals the chamber 178. In one embodiment, the processing tool 100 may include a plurality of processing volumes (which may be fluidly coupled together), where each processing volume has a different component 190. In one embodiment, a chuck 179 or the like may support a substrate 174 (e.g., a wafer, a workpiece, etc.). The substrate 174 may be at a distance D from the component 190. That is, the chamber 178 may be a vacuum chamber. In one embodiment, the component 190 includes a source array 150 and a housing 182. The source array 150 may include a dielectric plate 160 and a plurality of dielectric resonators 166 extending upward from the dielectric plate 160. Cavities 167 that enter the dielectric plate 160 may surround each of the dielectric resonators 166. The sidewalls of the cavities 167 are spaced apart from the sidewalls of the dielectric resonators 166 by a gap G. The dielectric plate 160 and the dielectric resonators 166 of the source array 150 may be an integral structure (as shown in FIG. 3D), or the dielectric plate 160 and the dielectric resonators 166 may be discrete components. The housing 182 includes a ring 131 that fits into the gap G. In one embodiment, the ring 131 of the housing 182 and the conductive body 173 are an integral structure (as shown in FIG. 3D), or the conductive body 173 and the ring 131 may be discrete components. The housing 182 may have an opening sized to accommodate the dielectric resonators 166. In one embodiment, monopole antennas 188 may extend into holes in the dielectric resonators 166. The monopole antennas 188 are each electrically coupled to a power source (e.g., a high-frequency emission module 105). Embodiments of the present disclosure utilize microwave processing. Without being bound by theory, the microwave processing described herein is believed to weaken the bonding of metal oxide materials with the assistance of the vibrational-rotational motion of metal oxide dipoles at microwave frequencies. The disclosed method utilizes an E-field for dipole rotation and a B-field for eddy currents, which results in heating of the metal oxide material without affecting other substrate materials. The energy of the microwaves can be adjusted low enough so as not to substantially damage dielectric materials (e.g., plasma-free, low-temperature). Additionally, the disclosed method is self-limiting by only affecting metal oxides and not affecting metal materials. Referring to FIGS. 5A and 5B, method 200 begins with metal oxide layer 260 on metal material 250. At operation 210, metal oxide layer 260 is exposed to microwave radiation. As used in this context, exposing a substrate to "microwave radiation" is understood to include activating a microwave source and exposing metal oxide layer 260 to the generated microwave radiation. In some embodiments, the microwave treatment does not produce a reactive plasma. In other words, in some embodiments, the metal oxide layer is not exposed to a plasma. Metal material 250 can comprise any suitable metal. In some embodiments, metal material 250 and metal oxide layer 260 comprise the same one or more metals. In some embodiments, the metal material comprises one or more of molybdenum, tungsten, ruthenium, copper, cobalt, tantalum, or titanium or consists essentially of one or more of molybdenum, tungsten, ruthenium, copper, cobalt, tantalum, or titanium. In some embodiments, the thickness of metal oxide layer 260 is in the range of about 20 Å to about 30 Å. In some embodiments, method 200 reduces the thickness of metal oxide layer 260 in the range of about 10 Å to about 30 Å, or in the range of about 20 Å to about 30 Å, or in the range of about 15 Å to about 25 Å. In some embodiments, method 200 reduces the entire metal oxide layer to pure metal. In some embodiments, the microwave treatment at operation 210 comprises exposing metal oxide layer 260 to an air flow. In some embodiments, the air flow is continuous and the microwave exposure is continuous. In other words, in some embodiments, neither the air flow nor the microwave source is pulsed during the microwave treatment. In some embodiments, the air flow comprises an inert gas. Without being bound by theory, it is believed that exposure to an inert gas flow can help facilitate the removal of volatile reaction by-products. In some embodiments, the inert gas comprises helium (He) or argon (Ar) or consists essentially of helium (He) or argon (Ar). In some embodiments, the inert gas comprises a hydrocarbon (e.g., CH 4 、C 2 H 6 、C 2 H 4 、C 2 H 2 ), or consists essentially of a hydrocarbon. In some embodiments, the inert gas comprises CO 2 or consists essentially of CO 2 ). In some embodiments, the gas flow includes reactants. Without being bound by theory, it is believed that exposure to the reactive gas flow can react with the activated oxygen atoms from the metal oxide layer 260 to form volatile species that are more easily purified from the processing chamber. In some embodiments, the reactants include one or more of hydrogen gas (H 2 ), or carbon monoxide (CO), or consists essentially of one or more of hydrogen gas (H 2 ), or carbon monoxide (CO). In some embodiments, method 200 is performed at a relatively low temperature. The relatively low temperature advantageously results in reduced damage to surrounding materials (such as, dielectrics). In some embodiments, the metal material is maintained at a temperature in the range of about 300 °C to about 400 °C. In some embodiments, the metal material is maintained at a temperature less than or equal to about 300 °C. In some embodiments, the metal material is maintained at a temperature in the range of about 20 °C to about 50 °C or in the range of about 20 °C to about 100 °C. In some embodiments, the exposure time period is controlled to reduce a predetermined depth of the metal oxide layer 260. In some embodiments, the time period is in the range of about 60 seconds to about 600 seconds, in the range of about 60 seconds to about 300 seconds, or in the range of about 30 seconds to about 120 seconds. In some embodiments, the power of the microwave array 140 is in the range of about 800 W to about 8000 W, or in the range of about 900 W to about 5000 W, or in the range of about 1000 W to about 3000 W. In some embodiments, the pressure of 178 can be controlled. In some embodiments, the pressure is maintained in the range of about 1 mTorr to about 10 Torr, or in the range of about 10 mTorr to about 1 Torr, or in the range of about 10 mTorr to about 100 mTorr, or in the range of about 50 mTorr to about 75 mTorr. As shown in Figure 5C, in some embodiments, the metal material 250 is located at the bottom 218 of the substrate feature 215. The feature 215 has sidewalls 214, 216. In some embodiments, at least a portion of the sidewalls 214, 216 includes a low-k dielectric 270. In some embodiments, the top surface 212 of the feature includes a high-k dielectric 280. In some embodiments, the high-k dielectric 280 includes silicon nitride. In some embodiments, the low-k material includes SiOC. In some embodiments, the low-k material of the sidewalls 214, 216 is substantially not damaged by method 200. As used in this regard, a dielectric is "not substantially damaged" if the normalized loss of carbon / silicon is less than or equal to about 30%. References to "one embodiment", "some embodiments", "one or more embodiments", or "an embodiment" in the specification mean that the particular features, structures, materials, or characteristics described in connection with the embodiments are included in at least one embodiment of the present disclosure. Thus, phrases such as "in one or more embodiments", "in some embodiments", "in one embodiment", or "in an embodiment" that appear in various places throughout the specification do not necessarily refer to the same embodiment of the present disclosure. Additionally, in one or more embodiments, the particular features, structures, materials, or characteristics may be combined in any suitable manner. Although the present disclosure has been described with reference to specific embodiments, those skilled in the art will understand that the described embodiments are merely illustrative of the principles and applications of the present disclosure. It will be apparent to those skilled in the art that various modifications and variations can be made to the methods and apparatuses of the present disclosure without departing from the spirit and scope of the present disclosure. Accordingly, the present disclosure may include modifications and variations within the scope of the appended claims and their equivalent elements. 100: Processing tool 104: Microwave source / High-frequency emission source 105: Emission module 106: Oscillator module 110: Voltage control circuit 120: Voltage-controlled oscillator 130: Amplification circuit / Amplification module 131: Loop 140: Array 142: Applicator 150: Source array 160: Dielectric plate 161: First surface 162: Second surface 165: Hole 166: Dielectric resonator 167: Cavity 170: Gas pipeline 172: Exhaust pipeline 173: Conductive body 174: Substrate 176: Chuck 178: Chamber 181: O-ring 182: Housing 183: Internal volume 188: Monopole antenna 190: Component 200: Method 210: Operation 212: Top surface 214: Side wall 215: Feature 216: Side wall 218: Bottom 250: Metal material 260: Metal oxide layer 270: Low-k dielectric 280: High-k dielectric To be able to understand the above features of the present disclosure in detail, the present disclosure briefly summarized above can be described more specifically by referring to the embodiments, some of which are shown in the accompanying drawings. However, it should be noted that the accompanying drawings only show typical embodiments of this disclosure and should not be considered to limit its scope, as the present disclosure may allow other equivalent embodiments. FIG. 1 shows a schematic diagram of a microwave processing tool including a microwave source according to one or more embodiments of the present disclosure; FIG. 2 is a schematic diagram of a semiconductor processing tool having a modular microwave source according to one or more embodiments of the present disclosure; FIG. 3 is a perspective view of a source array for a modular microwave source in accordance with one or more embodiments of the present disclosure. FIG. 4 is a cross-sectional view of a processing chamber for reducing surface metal oxides in accordance with one or more embodiments of the present disclosure; FIGS. 5A and 5B show an exemplary substrate during processing in accordance with one or more embodiments of the present disclosure; and FIG. 5C shows a cross-sectional view of an exemplary substrate in accordance with one or more embodiments of the present disclosure. For ease of understanding, wherever possible, the same reference numerals have been used to denote the same elements common to the figures. It is contemplated that elements and features of one embodiment may be advantageously incorporated into other embodiments without further recitation. Domestic deposit information (please note in the order of depository institution, date, number) None Foreign deposit information (please note in the order of depository country, institution, date, number) None 200: Method 212: Top surface 215: Feature 218: Bottom 250: Metal material 260: Metal oxide layer 270: Low-k dielectric 280: High-k dielectric

Claims

1. A method for processing a semiconductor substrate, the method comprising the steps of: exposing a surface of a semiconductor substrate to microwave radiation, the surface of the semiconductor substrate having at least one feature formed therein, the at least one feature having two sidewalls comprising a low-k dielectric material and extending a depth to a bottom, the bottom comprising a metal oxide layer on a metal material, wherein the microwave radiation reduces the metal oxide layer to the metal material.

2. The method as described in claim 1, wherein the metallic material comprises one or more of molybdenum, tungsten, ruthenium, cobalt, copper, tantalum, or titanium.

3. The method as described in claim 1, wherein the metal oxide layer is not exposed to a plasma.

4. The method as described in claim 1 further comprises the steps of: exposing the metal oxide layer to a gas flow while simultaneously exposing the metal oxide to microwave radiation.

5. The method as described in claim 4, wherein both the airflow and the microwave radiation are continuous.

6. The method as described in claim 4, wherein the gas flow comprises an inert gas.

7. The method as described in claim 6, wherein the inert gas comprises helium (He).

8. The method as described in claim 4, wherein the gas stream contains a reactant.

9. The method as described in claim 8, wherein the reactant is supplied at a flow rate in the range of about 1 sccm to about 50 sccm.

10. The method as described in claim 8, wherein the reactant comprises hydrogen (H2).

11. The method as described in claim 8, wherein the reactant comprises carbon monoxide (CO).

12. The method as described in claim 1, wherein the metallic material is maintained at a temperature in the range of about 300°C to about 400°C.

13. The method as described in claim 1, wherein the metallic material is maintained at a temperature less than or equal to about 300°C.

14. The method as described in claim 1, wherein the metallic material is maintained at a temperature in the range of about 20°C to about 100°C.

15. The method as described in claim 1, wherein the exposure time period is in the range of about 60 seconds to about 600 seconds.

16. The method as described in claim 1, wherein the low-k dielectric material is substantially undamaged by the method.

17. The method as described in claim 1, wherein the method reduces the thickness of the metal oxide layer in a range of about 15 Å to about 25 Å.

18. A method of processing a semiconductor substrate, the method comprising the steps of: exposing a surface of a semiconductor substrate having at least one feature to microwave radiation to reduce a molybdenum oxide layer on a molybdenum metal material, the at least one feature extending a depth from the substrate surface to a bottom containing the molybdenum oxide layer and having two sidewalls comprising a low-k dielectric material.

19. The method as described in claim 18, wherein the low-k dielectric material is substantially undamaged by the method.

Images